Search results

I don't have a 148 here at my house to look at, but it looks like the service manual schematic is wrong then also. I guess the 7.8 MHz does indeed enter at pins 7 & 8, with the ~34 MHz LO entering at pins 11 & 13. It's weird that both paper schematics that I have in my filing cabinet have this...

Both of those schematics show the signals entering on the same pins, the author of the first one just drew them in opposite places on the triangle. 11 & 13 are on the back in the official schematic, the redraw has them on the side for some reason. R191 is there to provide a current limited 8V-TX...

It just seems like a normal PNP power transistor to me, nothing special to see here. A reverse biased Base-Emitter junction acts like a zener diode with a fairly precise breakdown voltage. Most transistors are rated between 3-5 volts, but there are some rated higher. It's just not normally a...

Yeah, I suppose in a radio that uses the regulator in conjunction with the ALC to control the out power on SSB, that makes sense. My Magnum Deltaforce does this. When you turn the power wide open on SSB though, it fully saturates the regulator, so it just puts out slightly less than what's going...

That spec isn't too far off from normal. That's Emitter-Base voltage, which is typically around 3-8V. The Base-Emitter voltage is what's usually 0.6-1V. These are negative because it's a PNP transistor. In this case it means that if the Emitter voltage is more than 8V less than the Base, that...

The RP diode does absolutely nothing unless the radio is plugged in backwards, it's irrelevant to this conversation and it would have zero effect with a shorted regulator whether it's in circuit or not. It's before the regulator anyhow. It shouldn't be removed though. The combined resistance of...

The 45-50W dead carrier would be with a dual final Mosfet chassis. A dual final bipolar (1969/2312) won't do that much with a shorted regular, probably 35-40W, and something like a single final 66V will probably only hit 20W in that case. Keep in mind in AM mode with a full 14 volts on the...

Agreed LeapFrog, a shorted regulator in an RCI chassis just results in a 45-50W carrier with no modulation. Never hurt any drivers or finals that I've seen. They might want to put their radios in SSB mode with the power wide open because there should be 12-14V on the final collectors. It pulls...

Spot on brother. Been saying this all along. If the chassis/heatsink can't transfer the heat into the surrounding air, it doesn't matter how big of a transistor you put in there. Good article.

My IC-751 tunes 11m +/- a bit after a little RAM editing a few weeks ago. I'll give it a go and see if I can get anything. :cool: Hopefully we get some favorable conditions. 73s

The customer isn't always right, despite popular belief. That's just my humble opinion though. :censored:

I have a very old one that works great for what it is. I've talked skip from PA to Florida with it using only 20W continuous (80PEP) a couple summers ago when I had it on my old car. I did have a thin piece of plastic under the base to keep the metal from scratching the paint on the outside, and...

Just attach a huge rectifier directly to the 3 phase HV at your local substation to get your B+. (y)

If they are already within 5-10% (usually what ham radios specify for bias current tolerances), then no, you'd never notice the difference between that and a tightly matched set of the same part number. Now if you happened to get one that was unlucky and they were way off, such as the extreme...

What circuit though? What do you mean by balance resistor? Are we talking in a power combiner? Some circuits matter and some don't care. A Class-E switching RF amplifier doesn't really care at all about matching the Mosfets because they're being switched completely on and off. It operates more...

I've never had a 955 on my bench, so this will be an "on-paper" analysis based on experience with similar circuits, so a grain of salt should be added. The 955 has 4 identical Mosfets in it's final chain, setup in a 1 pre-driver into 1 driver into 2 linear PA section. The pre-driver and driver...

Building SMPSs is fun. That's how I got into electronics and radio in the beginning. Very cool.

I'm not confused at all, you seem to be missing the point. Bipolars and Mosfets do share some characteristics, load line theory calculations are one of those things. How the device is being driven doesn't particularly matter, voltage or current. Now, you are correct that as long as VGS(th) is...

Yes, and those tolerances can sometimes matter also. The higher the power and higher the frequency, the more it can matter, depending on what part of the circuit we're talking. They do matter much less though, and good designs will have reasonable tolerance acceptance factored into their...

How important it is to match FETs is very dependant on the circuit surrounding them. If you have a circuit like the amp in a Connex 4400-Turbo or a Galaxy 98VHP where you have 4 Mosfets all having their bias voltage set by a single adjustment POT, then matching of the VGS(th) _can_ be extremely...